These researchers are thinking about potential medical applications. I expect if studies show it to be safe and effective for humans, it's going to be used for movies and Halloween costumes and such.
New research harnessed the highly absorbent dye tartrazine, used as the common food coloring Yellow No. 5, to turn tissues in living mice clear—temporarily revealing organs and vessels inside the animals.
In mere minutes, smearing mice with a common food dye can make a desired portion of their skin almost as transparent as glass.
In a study published today in Science, researchers spread a solution of the dye tartrazine, a common coloring for foods, drugs and cosmetics, onto living mice to turn their tissues clear—creating a temporary window that revealed organs, muscles and blood vessels in their body. The procedure—a new form of a technique known as “optical tissue clearing”—has not yet been tested in humans, but it may someday offer a way to view and monitor injuries or diseases without the need of specialized imaging equipment or invasive surgery.
...
Scientists Make Skin of Living Mice Transparent with Dabs of Common Food Dye
New research harnessed the highly absorbent dye tartrazine, used as the common food coloring Yellow No. 5, to turn tissues in living mice clear—temporarily revealing organs and vessels inside the animals
www.scientificamerican.com